Alcohols
are a family of chemicals with slightly
different properties, depending on the number
of carbon atoms. A molecule of methanol
has a single carbon atom, ethanol has two,
and butanol four. Because of this, butanol
has a higher energy content (92% of that
of gasoline) than ethanol or methanol.
It is impossible to predict at this point
whether any of these three, or some combination,
will become a dominant and preferred fuel
option. All can be made from renewable biomass,
however, and thus all have a similar potential
to reduce oil consumption and improve environmental
quality.
Biobutanol – butanol made
from biomass – can be produced with
the same feedstocks as ethanol but with
a modified fermentation and distillation
process. Butanol can be used in standard
vehicles in gasoline blends up to 16%, and
it can be distributed by pipeline more easily
than ethanol, because it mixes less easily
with water. Like methanol, it is poisonous.
Butanol can also enhance low-level ethanol
blends by reducing their evaporative emissions.
Unlike ethanol, butanol can be easily blended
with diesel.
Recently, BP and DuPont announced that they
would partner to produce a “next generation”
of biofuels, beginning with biobutanol in
2007. Back to top
Methanol is commonly called “wood
alcohol.” It can be made from biomass
but is now chiefly made from natural gas.
Production of methanol is one way to make
use of remote natural gas that might not
otherwise be brought to market. It has about
half the energy content of gasoline and
about three-fourths the energy content of
ethanol.
Like ethanol, methanol is a high-octane,
high-performance fuel used by race car drivers.
Both methanol and ethanol can be used with
higher compression ratios than gasoline.
This can result in an increase in horsepower
of up to 15%.
The U.S. methanol industry has shrunk from
18 production facilities producing 2 billion
gallons of methanol per year in 1998 to
four facilities producing 300 million gallons
of methanol in 2005. Giant facilities are
being built where there is access to cheaper
natural gas, including Trinidad and Tobago,
Chile, Venezuela, and Oman. The fastest-growing
market for methanol in the world is in China,
which plans to build as many as 80 coal-based
methanol facilities.
• Unlike grain alcohol,
methanol is not suitable for drinking.
Indeed, its toxicity has led to concern
about its suitability for widespread
commercial use. (Fuel ethanol is made
undrinkable by the addition of 2-5%
gasoline.)
• Methanol fuel cells are seen
as a possible longer-lasting alternative
to batteries for laptop computers
and other consumer electronics.
Biobased alcohols can be blended
with isobutylene (derived from petroleum
or natural gas) to make liquid fuels called
ethers – methyl tertiary butyl ether
(MTBE) from methanol or ethyl tertiary butyl
ether (ETBE) from ethanol. These ethers
are attractive blending components because
of their high octane and because in blends
they reduce the volatility of gasoline,
decreasing evaporation and smog formation.
In addition, gasoline blended with ethers
can be shipped through conventional oil
pipelines.
For many years lead was used to increase
the octane of gasoline, and, when it was
phased out for health reasons, oil companies
chose to replace it with MTBE, starting
in 1979.
The use of MTBE increased in 1992 with the
introduction of new clean-air requirements.
Unfortunately, MTBE does not biodegrade
easily and has been found in ground water
throughout the country. In some instances
it has contaminated sources of drinking
water.
Even low levels of MTBE can make drinking
water supplies undrinkable due to its offensive
taste and odor. As a result, in September
1999, the EPA Blue Ribbon Panel on Oxygenates
in Gasoline recommended that the use of
MTBE be reduced substantially (with some
members supporting its complete phase-out).
Several states banned the use of MTBE, and
oil companies sought legal protection against
lawsuits involving MTBE. When Congress failed
to provide that protection in the Energy
Policy Act of 2005, the oil industry largely
abandoned MTBE and turned instead to ethanol.
ETBE is another alternative and is used
elsewhere, notably in France. However, ETBE
has not yet been adopted in the U.S., perhaps
because of uncertainty about its persistence
in the environment and concerns about its
effect on ground water.
